There is a need to couple optical radiation from large scale, high power sources into optical fibers. The radiation may be infra red, ultra violet, or visible light.
Optical fibers are used to conduct light to spaces which can not be directly viewed. For example, the inside of a hazardous material tank or internal regions of the human body would be viewed in this way. Optical fibers may also be used to conduct light to remote areas of a large liquid crystal display.
A high power optical radiation source is generally some kind of discharge lamp such as a microwave excited discharge lamp or an arc lamp. Discharge lamps can supply hundreds to thousands of watts of radiation. High power radiation is necessary for some applications for which it is desirable to use optical fibers as a means of conducting the light. Arc lamps emit in all directions, albeit not equally, except for the directions blocked by the electrodes and related structure. State of the art microwave lamps emit nearly equally in all directions. A microwave discharge lamp is disclosed in U.S. Pat. No. 4,485, 332 to Ury et al.
Since the known radiation sources emit in a large percentage of the solid angle space, some kind of optical system must be used to redirect the radiation towards the end of the fiber into which it is desired to couple the light.
According to usual practice fibers are cut squarely at their ends. In order to couple radiation into a fiber it must be made to impinge the end of the fiber at an angle no greater than 5 to 40 (the exact value is a fiber specification that varies from one fiber to another) degrees from the normal to the end of the fiber.
This requirement of the angle incidence of the radiation places a second requirement on the optical system employed.
The prior art has not provided a way to couple a large percentage of the radiation from a large scale radiation source into an optical fiber economically.
U.S. Pat. No. 4,950,059 to Roberts discloses a bulb which is reflective over its surface except for a small window through which light passes into a light guide. The light coupled into the light guide is not especially angled, and therefore it is unlikely that a bundle of optical fibers could be used instead of a light guide.
U.S. Pat. No. 4,850,669 to Welker et al discloses a parabolic section reflector used to couple light from an electric powered light bulb to an optical fiber bundle. Only a fraction of the solid angle of light emanating from the lamp would be focused by the reflector.
U.S. Pat. No. 4,792,692 to Herold et al. discloses an elliptical reflector which is used to couple light into an optical waveguide. The optical system disclosed does not direct a large portion of the light emitted by the source, which light is wasted.